Thermal mechanical processing of aluminum alloys (a)

ABSTRACT

THIS INVENTION IS CONCERNED WITH THE COMBINED THERMAL AND MECHANICAL TREATMENT OF AUMINUM ALLOY 2024 TO PRODUCE A HIGHLY UNUSUAL COMBINATION OF YIELD STRENGTH AND DUCTILITY. THE CHEMISTRY OF THIS ALLOY IS 4 1/2% COPPER, 1 1/2% MAGNESIUM, 0.6% MAGNESE WITH THE REMAINDER ESSENTIALLY ALL ALUMINUM. THIS ALLOY IS ALSO CONVENTIONALLY KNOWN AS SAE 24 AND 240. THIS TREATMENT YIELDS AN ALLOY HAVING A 0.2% YIELD STRENGTH OF 75,000 TO 85,000 POUNDS PER SQUARE INCH AND ULTIMATE TENSILE STRENGTH OF 85,000 TO 95,000 POUNDS PER SQUARE INCH AND AN ELONGATION IN A 2 INCH GAUGE LENGTH OF 8 TO 10%.   D R A W I N G

April w 17 E. GOLD 3,73%,725

THERMAL MECHANICAL PROCESSING OF ALUMINUM ALLQYS (A) Filed. March 22,, 1971 /WQ, 7P,

ATTORNEYS United States Patent 3,726,725 THERMAL MECHANICAL PROCESSING OF ALUMINUM ALLOYS (A) Edward Gold, Santa Ana, Calif., assignor to Philco-Ford Corporation, Philadelphia, Pa. Filed Mar. 22, 1971, Ser. No. 126,509 Int. Cl. C22f N04 US. Cl. Mil-12.7 2 Claims ABSTRACT OF THE DISCLOSURE This invention is concerned with the combined thermal and mechanical treatment of aluminum Alloy 2024 to produce a highly unusual combination of yield strength and ductility. The chemistry of this alloy is 4% copper. l'/z% magnesium, 0.6% manganese with the remainder essentially all aluminum. This alloy is also conventionally known as SAE 24 and 240. This treatment yields an alloy having a 0.2% yield strength of 75,000 to 85,000 pounds per square inch and ultimate tensile strength of 85,000 to 95,000 pounds per square inch and an elongation in a 2 inch gauge length of 8 to HISTORICALLY In the past the very moderate physical properties of pure aluminum have been improved by three specific and distinct processes. The first of these processes is the simple inclusion of a metaLas a solute in the aluminum and which provides a solid solution which is stronger than the aluminum alone. The second mechanism employcd in strengthening aluminum alloys is the so-called age hardening or precipitation process. In this process aluminum containing certain elements which are soluble in aluminum at elevated temperatures are put into solution in the aluminum by exposing it to such an elevated temperature and then quenching the alloy to produce a metastable solution. This metastable solution of alloying elements in aluminum is caused to precipitate either by long standing at room temperature or by artificially aging at elevated temperatures. The third method of improving the characteristics of aluminum alloys is by cold working to generate metal flow barriers in the usual manner.

It is known to combine the precipitation hardening and mechanical cold working to even further improve the physical properties of the alloy. Such a process is taught in the Pat. No. 3,133,839 granted May 9, 1964 to Gareth Thomas. No claim is made to this combination broadly.

TH E INVENTION The sole sheet of drawing in this case contains two photomicrographs of a specimen of aluminum Alloy 2024 produced in accordance with the teaching of this invention. These are transmission electron photomicrographs taken at 35,000x magnification.

Reference is made initially to the ASM Metals Handbook, volume 1, eigthth edition, pages 938, 939 and 940 for a very enlightening and detailed description of the known characteristics of this particular alloy. This alloy is also treated in some length in Machine Design, Feb. 12, 1970, at pages 50 ct sequor.

it has been discovered that aluminum Alloy 2024 can be given a combination of ductility and strength not heretofore available if it is subjected to the following treatment. These photomlcrographs appear to be characterized by a cell-like substructure containing very dense dislocation tangles interspaced with areas on the order of 1 micron of comparatively low dislocation density. There is an absence of the S Widmanstatten structure, and the dispersoids are not readily identifiable. They may have 3,726,725 Patented Apr. 10, 1973 been sheared and reduced in size and/or are masked from observation by the dense dislocation tangles.

Step 1 Completely solution treat the metal at a temperature of 9l0 to 930 F. for a period of time sufiieient to insure complete solution and then bring to room temperature quickly enough to avoid any decomposition of the solid solution.

Step 2 Heat the material at 365 to 385 F. for to minutes and again bring to room temperature before substantial further structural changes have occurred.

Step 3 Plastically deform the heat treated material 15 to 25%. This deformation may include such steps as rolling, forming, swaging, drawing or any convenient or necessary mechanical deformation.

Step 4 Thermally treat the deformed material at 290 to 310' F. for 25 to 35 minutes and again bring to room temperature rapidly enough to insure against structural change.

Step 5 Again plastically deform the material an additional 15 to 25% (measured as a percentage of the original starting thickness).

Step 6 Thermally treat this twice-worked material at 290 to 310' F. for 35 to 45 minutes and bring to room temperature quickly enough to avoid changes in the metallurgical structure.

The above-described heat treatment was executed successfully on inch thick sheets and water quenching was used to bring the thermally treated material to room temperature.

This material so treated exhibited a 0.2% yield strength of 75,000 to 85,000 pounds per square inch and ultimate strength of 85,000 to 95,000 pounds per square inch and an elongation in 2 inches of 8 to 10%.

Those skilled in the art will recognize that the precise thermal mechanical treatment outlined may be varied slightly from that described without departing from the scope of the invention or substantially deteriorating the properties of the final product.

I claim as my invention:

1. The process of thermally and mechanically treating an aluminum alloy containing copper, magnesium and manganese comprising exposing the aluminum alloy to a temperature of 910 to 930 F. for a period of time to complete the solution process, cooling the heat treated alloy to room temperature sul'ticienltly rapidly to prevent any substantial precipitation reactions from occurring, reheating the material to a temperature of 365 to 385 F. for a time period of 105 to 135 minutes to artificially age the alloy, plastlcally deforming the artificially aged alloy from 15 to 25%, again thermally treating the deformed alloy at 290- to 310' F. for 25 to 35 minutes, cooling the thermally treated alloy to room temperature aufliciently rapidly to prevent unwanted precipitation reactions from occurring, again plastically deforming the thermally treated alloy between 15 and 25% and finally again thermally treating the plastically deformed metal at 290 to 310' F. for a time period of 35 to 45 minutes and cooling the plastically deformed metal to room temperature 4 sufficiently rapidly to prevent unwanted precipitation re- References Cited 'acfionslo OCCUR d I 1 I d 1 UNITED STATES PATENTS 2. The process recite in c aim as app 1e to a umt- 2 083 576 6/1937 N k I A num Alloy 2024 and which produces a 0.2% yield 1 5 8,1965 f i 'g ii 4 strength Of 75,000 l0 35,00 pounds P61 sq are h, an 5 3 454: 35 7 1969 Jacobs 14 12 7 ultimate tensile stress of 85,000 to 95,000 pounds per square inch and an elongation in 2 inches of 8 to 10%. WAYLAND W. STALLARD, Primary Examiner 

